As exemplified by U.S. Pat. No. 5,122,905 to Wheatley et al and U.S. Pat. No. 6,982,025 to Bonk et al, it is known to produce interdigitated streams, for instance, of an repetitive ABAB layer configuration, in which A and B are rheologically diverse from one another. Certain of these composites are disclosed as providing advantageous optical properties. In the Bonk et al patent, other composites are disclosed as benefitting gas barrier use, cushioning, and resistance against flex fatigue. These composites include microlayers, and it is disclosed that these composites can be made by coextrusion.
U.S. Pat. No. 4,426,344 to Dinter et al is directed to a coextrusion process that includes the formation of layered composite streams having continuous, but nonplanar interfaces, by profiling the contact surfaces of merging streams. In accordance with the process, Dinter et al form the layered composite streams in different planes, and thereafter reposition the streams from a stacked orientation to an edge-to-edge coplanar relationship while reducing width, prior to joining the streams laterally. Thereafter in accordance with the process, the resulting fluid mass is extruded from a downstream die as a multilayered product. FIG. 2 of Dinter et al illustrates multilayered product consisting of two joined halves, as indicated by the phantom line in the Figure.
U.S. Pat. No. 5,094,788 to Schrenk et al, U.S. Pat. No. 5,094,793 to Schrenk et al, and U.S. Pat. No. 5,269,995 disclose technology by which a shaped layered stream of discrete and continuous layers of diverse thermoplastic materials is used to generate a plurality of interfacial surfaces in a molten polymeric mass. In this type of prior art, a shaped layered stream flowing in a direction designated z of an x-y-z coordinate system, and including a generally planar interface that lies in the x-z plane, is divided into a plurality of branch streams. The division into branch streams is along the x-axis, and is generally parallel to the z-axis. The x-axis defines a transverse dimension of the interface. Thus, a plurality of branch streams is produced by dividing an interface of a shaped layered stream; and the term “branch streams” as used in this art, means layered streams derived by division of a layered precursor stream.
Thereafter, the branch streams are reoriented relative to the x-axis and the y-axis, so that the branch streams are in a stacked orientation in the y-direction. The reoriented branch streams are combined in an overlapping relationship to generate interdigitated streams including a plurality of interfacial surfaces.
The '788, '793 and '995 type of prior art also discloses independently adjusting the flow rates of branch streams, and dimensionally changing streams in the x-direction and y-direction. In addition, the '995 patent discloses the use of protective boundary layers to avoid layer instability and breakup at interfaces in microlayer coextrusion, and thereby avoid adverse effect on desired optical and/or mechanical properties.
A drawback of the '788 and '793 type of prior art is that in the case of layered streams with adjacent layers of diverse Theological properties, interface distortion and hence layer deformation or distortion, may result from, for instance, time dependent migration. A further drawback of this type of prior art is layer interfacial instability; the use of protective boundary layers as in the '995 type of prior art, adds additional layers that may not be desirable for, or necessarily benefit, the intended use.
In addition, in the '788, '793 and '995 type of prior art, the resultant composite structures are limited to interdigitated layered structures. Also, layer distortion can be expected to be relatively greater with relatively more mechanical manipulation of shaped layered streams.
Accordingly, there is a need particularly when processing diverse thermoplastic materials, to form composite structures with reduced interface distortion, and thereby reduced layer deformation and distortion. Furthermore, there is a need to eliminate, or minimize the development of, layer interfacial instability, and it is desirable to achieve such a result without reliance upon protective boundary layers. It is desirable not only to minimize mechanical manipulation of shaped layered streams, but also to improve microlayer coextrusion.
Also needed are multilayered composite products including layers of improved performance, for instance, improved barrier layer performance or reduced stress-cracking, and multilayered composite products of more varied layer composition. The composite structure may be useful as a barrier, for example, as a gas, moisture or flavor barrier. Improved barrier performance will for instance, benefit pressurized bladders for footwear, as well as be advantageous in packaging of varied types.